NCT03972657 · Regeneron Pharmaceuticals
A Trial to Find Out if REGN5678 is Safe and How Well it Works Alone or in Combination With Cemiplimab for Adult Participants With Metastatic Castration-Resistant Prostate Cancer and Other Tumors
What this study is about
The main purpose of this study is to determine the safety, tolerability (how your body reacts to the drug) and effectiveness (ability to treat your cancer) of REGN5678 alone, or in combination with cemiplimab. The study has 2 parts. The goal of Part 1 (gradually increasing doses) is to determine a safe dose(s) of REGN5678 when it is given alone or in combination with cemiplimab.
View original scientific description
The main purpose of this study is to determine the safety, tolerability (how your body reacts to the drug) and effectiveness (ability to treat your cancer) of REGN5678 alone, or in combination with cemiplimab. The study has 2 parts. The goal of Part 1 (dose escalation) is to determine a safe dose(s) of REGN5678 when it is given alone or in combination with cemiplimab.
Interventions
DRUG
REGN5678
Administered as per the protocol
DRUG
Cemiplimab
Administered as per the protocol
Primary outcome measures
Incidence and severity of Treatment-Emergent Adverse Events (TEAEs)
Time frame: Through study completion, up to 5 years
Dose Escalation Phase
Incidence and severity of Adverse Event of Special Interests (AESIs)
Time frame: Through study completion, up to 5 years
Dose Escalation Phase
Incidence and severity of Serious Adverse Events (SAEs)
Time frame: Through study completion, up to 5 years
Dose Escalation Phase
Number of participants with Grade ≥3 laboratory abnormalities
Time frame: Through study completion, up to 5 years
Dose Escalation Phase
Incidence of Dose-Limiting Toxicities (DLTs)
Time frame: First dose through day 42 of last participant in each dose level
Dose Escalation Phase
Concentration of REGN5678 in serum over time
Time frame: Through study completion, up to 5 years
Dose Escalation Phase
Concentration of REGN5678 in combination with cemiplimab in serum over time
Time frame: Through study completion, up to 5 years
Dose Escalation Phase
Composite Response Rate (CRR) of 50% decline of Prostate Specific Antigen (PSA) and/or confirmed radiographic response of complete (CR) or partial response (PR)
Time frame: Through study completion, up to 5 years
Dose Expansion Phase - mCRPC cohort
Objective Response Rate (ORR) per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 criteria
Time frame: Through study completion, up to 5 years
Dose Expansion Phase - ccRCC cohort
Who can participate
This study lists these criteria on ClinicalTrials.gov. A study coordinator reviews eligibility during screening — this page does not determine whether you qualify.
Inclusion criteria
- mCRPC cohorts: 1. Men with histologically or cytologically confirmed adenocarcinoma of the prostate without pure small cell carcinoma. 2. Prostate specific antigen (PSA) value at screening ≥4 ng/mL that has progressed within 6 months prior to screening as defined in the protocol. 3. Has received ≥2 lines prior systemic therapy approved in the metastatic and/or castration-resistant setting (in addition to androgen deprivation therapy \[ADT\]) including at least: 1. one second-generation anti-androgen therapy (eg, abiraterone, enzalutamide, apalutamide, or darolutamide) 2. post-177Lu-PSMA-617 radiotherapy expansion cohort only. Must have received at least 2 doses of 177Lu-PSMA-617. ccRCC cohorts: 1. Men and women with histologically or cytologically confirmed RCC with a clear-cell component. 2. Diagnosis of metastatic ccRCC with at least one measurable lesion via RECIST 1.1 criteria 3. Has progressed on or after ≥1 line prior systemic therapy approved i
Where
- Gilbert, Arizona
- Phoenix, Arizona
- Tucson, Arizona
- Santa Monica, California
- Denver, Colorado
- New Haven, Connecticut
- Jacksonville, Florida
- Tampa, Florida
- Boston, Massachusetts
- Detroit, Michigan
- Rochester, Minnesota
- New York, New York
And 8 more locations — see the full list below.
Related conditions & keywords
Frequently asked questions
What is a clinical trial?
A clinical trial is a research study that tests new medical treatments, drugs, devices, or procedures to determine their safety and effectiveness. Trials are carefully designed and monitored to protect participants while advancing medical knowledge.
Is it safe to participate?
Clinical trials follow strict safety guidelines and ethical standards. Trials must be reviewed and approved, and participants are closely monitored by medical professionals throughout the study. You can withdraw at any time if you choose.
Will I be compensated?
Many clinical trials offer compensation for your time, travel expenses, and inconvenience. The specific compensation varies by study and will be discussed during the screening process. All study-related medical care is typically provided at no cost to participants.
Will I receive a placebo instead of treatment?
When effective treatment exists, participants typically receive either the standard treatment plus the study intervention, or the standard treatment plus placebo. You would not be denied effective care. Placebos are primarily used when no proven treatment is available, or in addition to standard care. Your trial consent form will clearly explain what treatments you may receive.
Can I leave a trial if I change my mind?
Absolutely. Participation in clinical trials is completely voluntary. You have the right to withdraw from the study at any time, for any reason, without penalty or loss of benefits to which you are otherwise entitled.
How long does a clinical trial last?
Trial duration varies widely depending on the study design and purpose. Some trials last just a few weeks, while others may continue for months or years. The study coordinator will provide specific timeline information during your screening call.
Data: ClinicalTrials.gov · synced Jul 9, 2026 · Source of record for eligibility and locations